Internet Explorer 11 has limited support for WebVTT files. Cues that indicate positioning and additional headers aren't parsed and may stop the track from loading altogether.
If the subtitles load on all other browsers, press F12 on IE11 and look at the Console tab for error messages.
A common cause for a WebVTT track to fail to load on IE11 is the error:
MEDIA12607: WebVTT Text Track: Expect 2 or more line terminators after file signature.
IE11 can only parse WebVTT files that start with the line "WEBVTT" followed by a blank line:
WEBVTT 00:00:04.100 --> 00:00:07.140
Amara's VTTs are compatible with IE11:
WEBVTT NOTE Paragraph 00:00:04.100 --> 00:00:07.140
The file failing to load on IE11 likely has additional headers immediately following the "WEBVTT" line, like:
WEBVTT Kind: captions Language: en 00:00:04.100 --> 00:00:07.140
Adding a blank line in between or deleting the additional headers will solve this issue.
We are limited in the amount of support we can provide for third-party software, but if you have more questions let us know and we’ll try to help. Send as much basic detail as you can to firstname.lastname@example.org.